Some results of seven studies of children's native Finnish language acquisition from 1971-1980 are summarized, focusing on two aspects: the main features in the development of Finnish inflection forms in 2-7-year-old children, and selected information derived from children's errors at the various age levels. Subjects were 260 children attending nursery schools, day care "clubs", and schools. Mastery of morphological forms were measured by tests using archaic (i.e., unfamiliar to the children) Finnish words, and some cognitive-linguistic skills were also measured with a variety of tests. Results indicated that the correct inflections are achieved gradually, as a result of the child's developmental level, the difficulty of the morphological form, and the linguistic and grammatical properties of the words to be inflected. Results also suggest that erroneous responses can offer psychologically valuable information about development, with the errors having different meanings in different age groups, revealing both linguistic progress and information about children's perception, processing, and interpretation of the tasks and approaches to solving cognitive and linguistic problems. However, more detailed research is needed to learn the strategies children use. Errors occurring in spontaneous speech were found not to have the same developmental meaning as those produced in a morphological test. (MSE)